At the dawn of the 15th century, Islam invaded Europe from the East and it seemed that Christendom itself was under threat of dissolution. In an attempt to save the Christian world, Holy Roman Emperor Sigismund called a conference at Constance, beside the Rhine, attracting the greatest minds in the Western world and innumerable princes, lawyers, and prostitutes. Here the author of The Four Nations: A History of the United Kingdom and Great Southern Land: A New History of Australia delves into this often overlooked conference and posits that it was one of the central moments in European history, calming Catholic schisms, stirring sparks of the Reformation, and heralding the dawn of the Renaissance.